This invention relates to a method for upgrading certain refinery streams and to the product obtained thereby. More particularly, this invention relates to a method for preparing an aromatic or naphthenic oil from such streams.
As is well known, several refining operations such as cracking and coking lead, either directly or indirectly, to the production of product streams which are relatively high in both polyolefins and aromatics. This is, of course, particularly true in steam cracking operations wherein the production of olefin is a principal objective.
As is also well known, in steam cracking operations, a hydrocarbon feed is, generally, combined with steam so as to form a feed mixture containing between about 0.5 and 10 mole % steam. The hydrocarbon steam feed is then subjected to an elevated temperature, generally between the range from about 1300.degree. to about 1700.degree. F. at a pressure, generally between about 1 and 5 atmospheres and for a holding time, generally within the range from about 0.1 to about 3.0 seconds. The actual desired product or products as well as the by-product or by-products which are obtained will depend upon the particular hydrocarbon feed and the steam cracking conditions actually employed. In this regard, it should be noted that at one point in time it was most common to employ various naphtha cuts in steam crackers for the purpose of producing olefin. More recently, however, heavier residual fractions and entire crudes have been fed to steam crackers for the purpose of producing both olefin and gasoline. The naphthas produced via this route, however, contain significant amounts of unstable reactive olefins and various aromatics which must be removed before the steam cracker naphtha can be used in gasoline blending. These materials are, of course, easily separated in a heat soaking operation which results in a mild, thermal polymerization of the polymerizable olefins and the polymerizable aromatics as well as some condensation to form aromatic rings. The product thus obtained is, commonly, referred to as a heat soaked polymer and has heretofore had a very limited utility.
Heat soaking so as to cause a mild, thermal polymerization of polymerizable olefins as well as polymerizable aromatics and condensation thereof as a means of upgrading various refinery by-product streams as well as a means for separating unstable compounds is, of course, well known in the prior art. For example, in copending application Ser. No. 422,096 which was filed Dec. 5, 1973 a new and novel process for upgrading at least a portion of a refinery stream is disclosed and claimed. In this process, a two-stage synthesis is implied and, again, the process stream which is treated was derived from a mild steam cracking operation for the production of linear alpha olefins.
Notwithstanding the general use of heat soaking operations, hydrogenation and hydrofining in the upgrading of refinery streams containing a relatively high concentration of alpha olefins and polymerizable aromatics, particularly those derived from steam crackers operated for the production of olefins, it has not, heretofore, been believed possible to upgrade similar streams obtained in steam cracking operations designed for the production of gasoline. In this regard, and as noted, supra, it has been known in the prior art to employ a heat soaking operation so as to separate unstable olefins and polymerizable aromatics from steam cracked naphthas. It is also known, for example, in U.S. Pat. No. 3,689,401 that by-product heavy fraction formed during the production of normally gaseous olefins in a thermal cracker is up-graded by hydrotreating and hydrorefining steps followed by further alkylation with alpha olefins obtained from other sources. Upgrading via these techniques is, however, generally considered too expensive and the cost thereof generally exceed the values of the upgraded products. As a result, it is not, at this time, considered expedient to employ such methods in the upgrading of by-product streams. As also indicated, supra, it is known that the product obtained from the heat soaking operation could be further modified and used as a core oil. The demand for oils of this type is, however, quite limited and, as a result, only a portion of these materials is used for that purpose. As a result, a large majority of the heat soaked polymer has in the past, been fed to catalytic crackers or similar refining operations for further processing. Generally, however, maximum advantage is not achieved by such further processing. In light of this, then, the need for an improved process for upgrading such by-products is believed to be readily apparent.